High frequency ignition system



Nov. 27, 1945. I Q R BEN I 2,389,637

HIGH FREQUENCY IGNITION SYSTEM Filed April 2, 1942 2 Sheets-Sheet 1' INSULRTIIM INVENTOR.

; Jamaal ffuen 'Nov. 27, 1945.v RUBEN HIGH FREQUENCY IGNITION SYSTEM Filed A ril' 2, 1942 2 SheeCs-Shee t 2 I IN VEN TOR. Jamaal Hahn W+CLL high potential difference.

.the magneto may practicallycease to function at mat-i Nov. 21, 1945 HIGfiFBEQUENCY IGNITION SYSTEM Samuel RubemNew- Rochelle, N-. r

Application April 2, 1942, Serial No. 431,322

This invention relates to ignition systems for internal combustion engines.

An object of the invention is to improve high voltage ignition systems.

Another object is to improve the timing of ignition and produce a system whose timing remains constant over long periods of use.

A further object is to improve high altitude isnition systems, such as are used in aircraft, and to reduce or eliminate the ignition difficulties frequently encountered at high altitudes, such as corona discharge and electric breakdown of the "system.

An additional object is to improve the operation of ignition systems under conditions of adverse spark plug fouling. I

Other objects of the invention will be apparent from the following description and accompanying drawings takenin connection with the appended claims.

The invention comprises the features of construction, combination of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrations in the draw s,

In the drawings:

Figure 1 is a circuit diagram of an ignitio system for a nine cylinder airplane engine, embodying features of my invention;

Figure 2 is a simple diagram of the equivalent circuit of the .high frequency portion of the system; and

Figures 3, 4, 5, 6, '7 and 8 illustrate modifications of the system.

One of the principal limitations on high altitude flying has been the difficulty of providing ignition systems for airplane engines which are not subject to electric breakdown due to the rarefication of the .air at high altitudes. The low atmospheric pressure at these altitudes permits corona discharges to develop between points of In magneto systems times due to flash-over in the magneto itself The high tension cables in the distributor manifold and leading from the magneto to the manifold also break down unless shielded in proper type of cables. The distributor also is subject to arc-over and disruption of proper timing at high elevations.

Another problem with ignition systems has been the gradual variation in the timing conditions of the circuit due to contact or cam wear.

11 Claims. (Cl. 123-148) A further di'fliculty has been the failure of the spark plugs to function-properly when fouled by carbon due to cold plugs.

The system of the present invention utilizes a high frequency circuit and obtains accurate timing by use of an element fonvarying the resonance of the circuit to obtain acqirate timing of the spark discharge. The system' also has the resonant elements so arranged that the high voltage necessary for sparking is confined to a small section of the circuit adjacent to .the spark plugs, the majority of the distribution circuit operating at a relatively low voltage at which disturbing effects at high altitudes are not encountered.

The system produces an ignition yoltage of high frequency and steep wave front so as to effect sparking of the plugs even under conditions of adverse plug fouling.

The system also does away with the necessity for a distributor of the type using a spark gap between the rotating contact and the stationary terminals and enables the substitution of a direct contact type of distributor. The distributor is not required to make and break any substantial current, however, as the plug voltage is generated only when the distributor is in the middle of its contact position with any of the stationary terminals.

The system also allows the use of larger sizes of spark plugs for all operating conditions, thus improving the maximum power development of the engine during take-off and other periods of peak performance requirements. Y

In the past where high frequency systemshave been used they have depended upon the use of a high frequency transformer to apply the voltage to the spark plug. This required a fairly high voltage transmission to the primary to avoid excessive or impractical transformer ratios and unless the transformer was close to the plug insulation and distributed capacity loss was effected.

In my system, due to the fact that the high potential is developed across a resonance circuit composed of an inductance and capacitance at high frequency, the inductance and capacitance can be of low values and small size. Due to the phase relation across such a series resonance cirmat the total voltage across both due to resonance cancel each other. Thus a low applied voltage can be transmitted through the distributor and manifold and be resonated up to a high oscillating potential, such as 10,000 volts across a relatively small capacitance.

The timing is efiected in the be'stpractical manner by varying the inductance in the radio frequency circuit. This is best accomplished by establishing resonance as the point when the variable inductance has minimum inductance. Another advantageous factor in doing this in this manner is that it allows only one spark train for a given angular position of the timing device.

Referring to the drawings, Figure 1 shows an ignition system utilizing features of my invention as applied to a nine cylinder radial airplane engine. The source of electric energy for the ignition system comprises a generator or alternator III which generates a low or intermediate frequency alternating current as indicated by curve A shown immediately below the generator in the circuit diagram. The frequency of the alternator is preferably sufficiently high to insure several oscillations at each sparking period. Thus an alternator capable of generating 3,000 cycles per second at an intermediate engine speed might be suitable. The alternator or generator should also preferably be of the type which will produce a substantially constant output voltage at all speeds.

The alternating current generated by alternator 'I 0 isstepped up by low frequency transformer I I to produce an alternating potential of higher voltage across the secondary of the transformer as indicated by curve B shown immediately under the transformer -in Figure 1. Transformer H is designed to have a rising voltage characteristic with increase in frequency. A

quenched spark gap [2 is connected across the terminals of the transformer secondary winding and a series circuit'consisting of a condenser I3 and' the primary winding of a high frequency transformer I4 is connected in shunti with the spark gap. The alternating voltage across the secondary of low frequency transformer ll results in a periodic breakdown of spark gap 12, thereby generating damped oscillations in the oscillatory circuit including condenser l3 and the primary of high frequency transformer I4. These oscillations may be somewhat of the form illus;

I trated in curve C in Figure 1 and have a characteristic frequency determined by the constants of the circuit such as capacitance I3 and inductance of the transformer I4.

The secondary winding of high frequency transformer I 4 has one terminal grounded, the other evenly distributed inserts ll of pressed iron powder or the like distributedaround its periphery. The disc is driven by the engine at one-half the engine speed so that segments l'l move past a pole face of the core of inductance I6 at a speed corresponding to the sparking frequency of' the engine.

Distributor I9 comprises a ring 2| of molded plastic or other insulating material having nine molded-in segments 20 distributed about its inner periphery. The inner periphery is cut with gear teeth and the end of rotating distributor arm 22 carries a small pinion gearcontact 23 which rolls around the inner periphery of the ring, thus making contact with one segment after another in sequence. Rotating arm 22 of the distributor is also driven at one-half engine speed and maybe mounted on the same shaft with disc ll of the inductive timer.

The segments 20 of the distributor are connected by individual conductors 2! through the cable manifold 25 to high frequency inductances 26 adjacent to individual spark plugs 23 of the engine. The other end of each inductance 28 is connected to the center electrode of its associated spark plug 28. A condenser 21 is associated with each coil 26 and is connected between the center electrode and the ground electrode of the spark plug. High frequency coil 26 is provided with a powdered iron core 26a which is adjustable to a certain extent to enable adjustment of the resonance frequency of the circuit.

By reference to Figure 2, it will be observed that a high frequency resonant circuit is formed by transformer secondary Hs, variable inductance I6, high frequency inductance 26 and capacitance 21. As this circuit is brought into resonance with the high frequency oscillations applied through transformer M from the quenched spark circuit by variation of inductance IS, the circuit will oscillate in such a manner as to develop a high oscillatory voltage at point P at which the spark plug is connected. This voltage is sufficient to produce a spark discharge across the electrodes of the spark plugs. With this circuit it will be observed that the high voltage is developed only in a comparatively small section of the circuit adjacent to the spark plug, the balance of the circuit operating at comparatively low voltages. Thus the entire circuit from transformer I4 to coil 26 is at low voltage including the cable manifold.

Variation in the inductance of winding I6 is produced by variation in the proximity of rotating segments I! on rotor l8. While it is possible to adjust the circuit for resonance to the point of maximum or of minimum inductance in coil [6, it is preferred that the point of minimum inductance be used for resonance and the circuit be thrown out of resonance as the inductance of the coil is increased.

To summarize the operation of the system, the alternator I0 supplies an alternating current of low or intermediate frequency to the transformer .II which steps up the voltage to a value necessary to initiate a discharge across quenched spark gap l2, thus setting up high frequency oscillations in the circuit comprising the spark gap, capacitance I3 and the primary of high frequency transformer I 4. The turn ratio and the coupling of the oscillation transformer H is such that when resonated it will apply adequate sparking voltage at the spark plugs. Distributor l9 connects the secondary circuit periodically to each of the spark plug circuits. 'At the time rotating contact 23 of distributor I8 makes contact with any segment 20, the circuit is-out of resonance and hence no substantial current flow occurs at the instant of first contact. When distributor contact 23 reaches substantially the middle of a stationary segment, the core of coil l6 reaches a point substantially midway between two of segments I1 on the timer rotor which is a point of minimum inductance and brings the circuit into resonance. As the circuit is brought into reso nance, it will oscillate under the impulses received from the quenched spark circuit, thus developing a high oscillatory voltage across condenser 21 and the electrodes 'of the spark plug producirig the discharge of condenser 21 through the spark plug.

The spark may be advanced or retarded in relation to the engine cycle by rotating frame I! of the timer slightly to change the position of the core of inductance IS with respect to the rotating segments of the rotor.

A preferred frequency for the high frequency oscillations is 100,000 to 300,000 cycles per second, the oscillation circuit being designed to prevent excessive losses due to distributed capacitance, resistance and the like in the useful frequency range.

Figure 3 illustrates a circuit for the most part similar to that of Figure 1 but differing from it in the use of a variable condenser M for timing in place of the inductive timer of Figure 1. In this circuit a fixed capacitance 30 is connected in series between the secondary or high frequency transformer i4 and timer is and a relatively small variable condenser iii is connected in shunt with condenser 30. Condenser 3| may comprise, as illustrated, three evenly spaced stator plates 32 and a three arm rotor 33 which is rotated at one and one-half times the engine speed, thus bringing the circuit into resonance at the proper rate for periodic sparking of the engine. The rotor it may preferably run in a liquid of high dielec= tric constant to increase the capacity of the condenser.

Figure 4 illustrates amodiflcation wherein the rotary timer M is located in the quenched spark circuit of the ignition system where it varies the inductance of winding 4| in series with the primary of high frequency transformer M. This arrangement produces very sharp tuning as the inductance located at thi point suppresses frequencies other than those which are in resonance.

The high voltage coil -26 and condenser 21 which are located adjacent the spark plug may be mounted directly on the plug or may be located at the terminal of the cable manifold to which the plug is connected.

The core of the periodically varying inductance is preferably formed of iron powder of low loss and small grain size. can be encased in a pressed iron powder shield and return path to afford a greater inductance variation and sharper minimum inductance points when the rotor segments pass the core ace.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the ,spirit and scope of the appended claims.

What is claimed is:

1. An ignition system comprising a source of oscillations, a plurality of series resonant lines each developing a high oscillating voltage in one section thereof, the remainder of each of said lines remaining at a lower voltage, a spark plug connected to the high voltage section of each line, and a variable impedance for bringing said lines individually into resonance with said oscillations in sequence.

2. In an ignition system, a source of oscillations, a series resonant line fed thereby, said line developing a high oscillating voltage in one section thereof in response to said oscillations while Figure 5 shows a modification wherein the condenser it of the quenched spark circuit is replaced by fixed condenser 50 shunted by variable condenser 5| having fixed plates 52 and a rotor 53 driven by the engine to vary the resonant 'irequency of the circuit.

Figure 6 illustrates a modification in the quenched spark circuit, the spark gap 6| in this instance being connected in series with the primary of high frequency transformer l4 and condenser 80 being connected across the secondary of low frequency transformer I I.

Figure 7 illustrates acircuit suitable for dual ignition wherein alternator l0 supplies low frequency alternations to the primary I2 of a low frequency transformer II having two second-- the ignition circuit including variable inductance 82 varied by rotary inductive timer 83.

the remainder of said line remains at lower voltage, and a spark plug connected to said section of high voltage. v

3. In an ignition system, a source of oscillations, a series resonant circuit fed thereby and comprising a capacitance and an inductance in series, and a spark plug electrode connected to the common terminal of said capacitance and inductance.

4. In an ignition system, a source of high frequency ,energy, a plurality of sparkplugs and a plurality of series resonant lines, each having, when resonated, a point of high oscillatory voltage, each of said spark plugs being connected to the high voltage point of one of said lines, a distributor for periodically connecting said high frequency source to said lines in sequence and a periodically varying impedance in the common portion of said system preceding said distributor 4 for bringing said lines into resonance with said Instead of using an alternator I0 driven by the internal combustion engine, it is contemplated that in some instances a motor-generator set may be used to produce the low frequency a]- ternations.

It is also contemplated that other sources of tact operated transformer.

source while they are connected thereto by said distributor.

5. In an ignition system, an energized oscillatory circuit, a second oscillatory circuit coupled thereto, said second circuit comprising a series resonant circuit, having, when resonated, a point of high oscillatory voltage, a spark plug connected to said point of high voltage, and a periodically varying impedance in one of said circuits for varying its natural frequency and periodically bringing said circuits to the same oscillatory frequency to produce resonance in said second circuit and resultant sparking of said plug.

6. An ignition system comprising a source of high frequency oscillations, a. spark plug and a resonant line connecting said source to said plug, said line including a cable conductor extending from said source to the vicinity of said plug, a high frequency inductance connected between said conductor and the ungrounded electrode of said plug, and a capacitance connected in parallel with the electrodes of said plug, said resonant The core and its winding line developing a high oscillatory voltage across said plug, whilesaid cable remains at a relatively low voltage.

7. An electric ignition system comprising a source of high frequency oscillations, an im-' pedance fed thereby, a distributor. and a plurality of high frequency lines having spark plugs associated therewith connected periodically by said distributor to said impedance and forming oscillatory circuits therewith, said impedance including a periodically varying-reactance for bringing said lines into resonance with said source while they are connected thereto by said distributor.

8. An electric ignition system comprising an energized oscillatory circuit. an ignition distribution circuit, a coupling impedance coupling said distribution circuit to said oscillatory circuit, said distribution circuit comprising a distributor and a plurality of high frequency lines having spark plugs associated therewith connected periodically by said distributor to said coupling impedance to form resonant circuits therewith, said oscillator circuit including a periodically varying reactance for bringing said oscillatory circuit to the frequency of said resonant circuits while assaea'r 7 tributor to said variable inductance to form gel onant circuits therewith, spark plugs conn to said lines, and an inductance varying ,element driven by said engine for varying said inductance to bring said resonant circuits into resonance with said oscillatory circuit.

10. An ighition system for an internal combustion engine comprising a relatively low frequency A. C. source, a discharge device periodically discharged thereby, a tuned oscillatory circuit oscillated by the discharges in said device. said oscillatory circuit including a periodically varying inductance for varying the oscillatory fre-' quency thereoi,-acoupling device, and-an ignition distribution circuit coupled to said tuned circult thereby, said distribution circuit comprising a distributor and a plurality of high frequency lines periodically sequentially connected by said distributor to said coupling device to form resonant circuits therewith, spark plugs connected to said lines, and an inductance varying element driven by said engine for varying said inductance to bring said oscillatory circuit to the resonan frequency of said resonant circuits.

11. An ignition system for an internal combustion engine comprising a high frequency vacuum tube oscillator, an ignition distribution circuit coupled thereto, said circuit'comprising a distributor, a periodically varying-inductance and a plurality of high frequency lines periodically sequentially connected by said distributor to said varying inductance to form resonant circuits therewith, said inductance bringing said circuits into resonance at the frequency of said oscillator while each line is connected by said distributor.

SAMUEL RUBEN. 

